Solidification and transformation behaviour of Cr-Ni stainless steel weld metals with ferritic single-phase solidification mode: Study of solidification and transformation of Cr-Ni stainless steel weld metals (4th report)

Summary

This paper describes an investigation of the microstructural changes taking place in Cr-Ni stainless steel weld metals exhibiting ferritic single-phase solidification behaviour from the solidification stage down to room temperature. These steels initially show precipitation of the austenite at the ferrite grain boundaries on cooling. Continuous intergranular austenite is then formed by the coalescence of globular austenite along the grain boundaries. The austenite has the Kurdjumov-Sachs crystallographic orientation relationship (K-S relationship) with the ferrite on both sides and selects different combinations of close-packed planes and directions for each ferrite. Widmanstätten austenite, which has the same crystallographic characteristics as the intergranular austenite, subsequently grows into ferrite grains. In duplex stainless steel weld metals containing nitrogen, intragranular austenite precipitates after the formation of intergranular austenite. Nitrogen diffusion primarily controls the precipitation of both intergranular and intragranular austenite. With increasing Cr and Ni contents, precipitation of intragranular austenite increases because of an increase in microsegregation during solidification.